Most turbines in use today are of either the impulse or the reaction types. Such turbines have demonstrated satisfactory performance but, particularly because of the high stresses to which they are subjected, their manufacture requires use of exotic materials and fabrication techniques. Some work has also been done with cohesion type turbines wherein a series of discs are driven by friction of a fluid or saturated vapor at high speed across these surfaces. However, such turbines have seen only limited success.